When the seat of the pants are either too stretched out or there's not enough booty to fill the pants, the extra fabric is booty slack.
Jennifer: Hey, Cheryl, check out John today!
Cheryl: Well, he looks damn good, but he's got too much booty slack.
Cheryl: Well, he looks damn good, but he's got too much booty slack.
by Whitening toothpaste March 2, 2014